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Soda stream bubbling (Classroom experiment)

Soda streams use carbon dioxide (CO2) to make drinks fizzy. When you drink fizzy drinks you are drinking liquid that has been “carbonated”, which means it has had CO2 bubbled into it so that it becomes saturated with gas. The gas stays as a gas because there is so much of it in the liquid – this would even happen in our experiment and in the sea if we were to add enough CO2, but it would take a lot!

Once the bottle of fizzy liquid is opened the drink becomes flat because eventually the gas escapes out of the water into the atmosphere. In a half full bottle of fizzy liquid, some of the gas in the liquid will escape into the empty space in the bottle until both have reached an equilibrium state. When the bottle is opened there is a fizzing sound as all the built up pressure is released from the bottle.

If you are able to get hold of a soda stream you can try your own CO2 experiments (adult supervision required):

Try bubbling different amounts of CO2 into a liquid (preferably seawater, but ordinary water will work too) and test the pH of each trial. What do you find? What happens to the pH over time, as the gas leaves the liquid? You can ask us what should happen on the Ask a Scientist page…

Get some chalk (ordinary chalk for writing on boards will work) and try putting these into each of your bubbled liquids to see what happens to it – to be scientific you should weigh each piece of chalk before you put it in and then weigh it again after a certain period of time.

Chalk is made of the same material, Calcium Carbonate, as the shells and skeletons of many marine organisms. In fact the chalk cliffs that are seen around our coastlines (White cliffs of Dover, UK & White cliffs around Calais, France) are made up of the protective plates (liths) and shells of microscopic planktonic organisms like coccolithophores and formanifera.